Exterior Caulk and Caulking Q&A

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Dear NH,

Do you caulk all of the joints between the vertical boards of vertical board
siding when prepping to paint a house? Or is it like horizontal clapboards,
which are left uncaulked at the laps, to allow moisture to escape?

RE

RE,

First, a disclaimer. I am no fan of vertical siding since it just does not do
a great job preventing water from seeping into the wall as does horizontal,
overlapping siding. I have seen too much wood rot encouraged by this visually
attractive but functionally deficient siding. I don't have a place in my big
heart for it!

In my opinion, caulking between the seams in any lapped siding (either
horizontal or vertical) is not good practice but not just because of any
potential vapor barrier effect. The siding expands and contracts with
temperature and humidity. Think of a wood home as a living thing. It needs to
move and breathe. When you try to restrict either it is at your peril!

Caulk, by its adhesive nature, will try to limit this movement, leading to
widespread failure and cracking in the caulk over time. This will in turn be
unsightly and not amenable to easy repair, adding to the prep workload when
repainting. This is not to imply that caulk has no place in paint prep! Places
where dissimilar materials meet and around window and door frames are two
examples of areas needing proper caulking.

The other issue is the sheer volume of the caulk that would be needed to
accomplish this job. And, barring the rental or purchase of bulk caulk and air
compressor-powered caulking equipment, the time and energy needed to do such a
job would also be prohibitive.

If the home has been properly constructed, and there is a "housewrap" of some
kind under the siding to prevent exterior moisture from reaching the framing,
you should not have a need to even consider any further weatherproofing outside
other than a quality paint or stain job.

Aside... many people do not know this, but siding, shakes and clapboards
should be pre-sealed on both sides prior to installation (or at least the
inside), unless this is done at the factory. Once installed, it is
impossible to seal the inside but it can nevertheless be victim to moisture and
rot!